Conventionally, there is a computer system that provides a large-scale data storage service to a host apparatus. The system is known as a system comprising a host apparatus, a storage apparatus (also called a storage system) connected by the host apparatus, and a management apparatus of the storage apparatus.
The storage apparatus manages a plurality of hard disks by a RAID (Redundancy Array of Independent/Inexpensive Disks) system. Physical storage areas included in a multiplicity of hard disks are made logical, and the areas are provided to the host apparatus as logical volumes. The host apparatus accesses the logical volumes to request reading/writing of data.
An example of the logical technique includes so-called thin provisioning (Thin Provisioning). Physical storage areas are not included in the thin provisioning, and logical volumes with virtualized storage capacity are set to the host apparatus. The logical volumes are called virtual volumes, and the storage apparatus sequentially allocates the storage areas to the virtual volumes in accordance with the write access to the virtual volumes by the host apparatus. Therefore, the technique is advantageous in that the storage resources can be effectively used, compared to a system of allocating large-capacity storage areas to the logical volumes from the beginning.
The thin provisioning is described, for example, in Patent Literature 1 to 4. In the thin provisioning, a section which provides the storage areas to the virtual volumes is configured to store write data by allocating the storage capacity from a capacity pool including real storage areas to addresses of the virtual volumes when there is a write access from the host apparatus to the virtual volumes. The “capacity pool” (also simply called “pool”) is defined and set by, for example, compiling a plurality of logical groups with real capacity to be used for writing in the virtual volumes, and the plurality of logical volumes belonging to the pool are called pool volumes.
Patent Literature 5 discloses a technique, in which whether the access frequency to stored data is high or low is determined, and if the access frequency is high, the data is moved, within the pool, to a pool volume including a medium suitable for high-speed processing based on physical characteristic information (such as the type of medium and the number of rotations of the disk) of media of the pool volumes.